A keyless entry system is well known in which doors of vehicle are locked or unlocked if the system receives a wireless signal which is transmitted when a switch of a mobile terminal (i.e., an electronic key) is operated by a user and an ID code included in the wireless signal is valid.
Recently, a smart key system is known from JP2004-359057 A, for example in which the system performs a bi-directional communication with feeble electromagnetic waves between a transmitter-receiver installed in the vehicle and the mobile terminal, detects an approach of a valid user toward the vehicle by ascertaining the ID code of the mobile terminal, and unlocks the doors of the vehicle concurrently with a detection of an operation of a door outer handle. In such a type of a smart key system, the communication is also performed after the user opens and closes the door, and if the valid ID code of the electronic key is ascertained again, an immobilizer function is deactivated and a steering wheel lock is released. After that, the user can turn on an ignition switch by manually operating a dial switch or the like to start an engine without inserting the electronic key into an ignition cylinder. Further, in this smart key system, the communication is also performed when the user turns off the ignition switch and then opens and closes the door, and if the electronic key with the valid ID code is detected to move away from the vehicle, the above-mentioned various devices are locked. In this way, in the smart key system, if the user has the electronic key, various manual operations using the electronic key become unnecessary and thus the convenience is enhanced.
In such the smart key system, since the communication with the electronic key is performed on the condition that the user rides in or gets out of the vehicle (accompanied by opening and closing operations of the door) as mentioned above, it becomes an important factor to determine whether the opening and closing operations of the door are performed. In particular, recently, such a system is proposed in which an operation of a motorized steering wheel lock is performed in connection with the detection of the opening and closing operations of the door, and thus information from a door courtesy switch is utilized to implement more functions.
In general, the opening and closing operations of the door is detected based on an ON/OFF signal of the door courtesy switch which is attached to the door, etc. An abnormality (including a failure) of the door courtesy switch causes an abnormality of a system which uses the information from the door courtesy switch, and further may cause a key trapped situation in which doors are locked due to an automatic lock function, for example, while leaving the key in a cabin of the vehicle. It is noted that the automatic lock function is a function which automatically performs the door lock operation if a predetermined time period (30 sec, for example) has passed without the opening and closing operations of the door being detected after the door unlock operation is performed in connection with a wireless signal in the keyless entry system or the smart entry system, for example. Normally, if the door courtesy switch is normal, the automatic lock function is not activated even if the user unlocks the door, opens the door to get out of the vehicle, closes the door while leaving the key in a cabin of the vehicle, and moves away from the vehicle in order to go back home for getting something the user left, for example. However, if there is an abnormality of the door courtesy switch, the opening and closing operations of the door by the user is not detected and thus the above-mentioned key trapped situation may occur.
JP2003-297166 A discloses a door courtesy switch abnormality detection method in which the door courtesy switch is configured in such a manner that a voltage status of a wire harness connected to the door courtesy switch becomes different between an abnormal state and a normal state. In this arrangement, whether the door courtesy switch is normal or abnormal (i.e., open circuit and short circuit of the wire harness) is detected by monitoring the voltage status of the wire harness.
A permanent abnormality of the door courtesy switch such as open circuit and short circuit of the wire harness can be detected by an ordinary diagnostic tester. On the other hand, a connection failure or the like of the door courtesy switch is likely to occur temporarily. For example, there are many cases where a connection failure or the like of the door courtesy switch occurs temporarily due to a foreign substance involved or a hardening of grease at low temperature. Such type of abnormalities is not likely to be detected by the diagnostic tester. However, even such a temporary abnormality may cause an abnormality of a system which uses the information from the door courtesy switch, and detection of such a temporary abnormality is useful in terms of abnormality analysis.